A stimulus is said to be inhibitory when a high probability re- sponse is not emitted in the presence of the stimulus. The primary goal of the proposed research is to determine whether inhibition occurs after discrimination training with errorless methods (i.e., with pro- cedures in which incorrect responses are not emitted of training with extinction (i.e., with incorrect responses) to errorless training on two types of inhibition tests, the additive cues test and the resis- tance to reinforcement test. In addition, the research will compare the blackout method and the fading method of errorless training. Data from this research should provide information on basic effects produced by various types of discrimination training.